A disadvantage of existing fill valves is that they typically turn on (and start refilling the tank) at exactly the time when the water level first drops and the flush starts. The disadvantage with this approach is that the tank refilling starts while the flush valve is still open (and the water is still draining out of the tank). Although the flush valve closes quickly when the tank finally empties, all of the water supplied into the tank by the fill valve during the time when the flush valve is open is simply lost. It would instead be desirable to delay the start of the refilling until after the fill valve has fully closed. This would conserve water resources.
Unfortunately, current systems that try to delay the turning on of the fill valve until after the flush valve has closed have various disadvantages. For example, they tend to have too short a delay, or they have complex moving parts that can get fouled with hard water deposits and become ineffective over time. It would instead be desirable to provide a simpler refill delay solution that does not rely on complex mechanical linkages and moving parts.
Yet another problem common to existing fill valves is small leakage in the tank. Leaks can be small or large. A small leak in the tank will cause the water level in the tank to slowly drop. Unfortunately, this slight drop in water level immediately turns the fill valve on. Since only a partial re-filling is needed, the fill valve will then quickly shut itself off. Between flushes, the tank is almost completely filled. As a result of the tank being ostensibly filled, a user may not be able to recognize that the flush valve is leaking. A leaky flush valve that goes unrepaired will waste water which is of particular concern in an age when water has become increasingly scarce and expensive. To save water, and to reduce fill valve operation times, it would instead be desirable to permit small leaks without having to turn on the filling valve.
Conversely, large leaks are also a problem. Large leaks can be caused by a stuck (open) flush valve or by a cracked tank. When the refill rate of the fill valve is less than the leak rate from the tank, the fill valve will remain on, but the water will simply drain down into the toilet bowl, with the tank never re-filling. This situation can waste a huge volume of water, and cause a homeowner to suffer considerable expense. Current systems do not effectively deal with this problem at all. Therefore, there is a need for a fill valve that turns itself off when a large leak in the tank occurs.